The present invention relates to a fail safe electrically powered actuator for a damper, valve, elevator or other positioning device, and more particularly to a mechanical return which combines with an electrical motor to fail safe proper positioning of the device when normal power conditions have failed.
Heating and/or cooling control valves and dampers are currently positioned using pneumatic, electric or electronic actuators. Pneumatic actuators inherently adopt a fail safe position, and many electronic and electric actuators are designed to take a fail-safe position should electrical power be lost or switched off. In electric/electronic actuators the methods of accomplishing this include springs, capacitors, gravity (weights) or batteries with adequate power to return the valve or damper to that normal position on loss of electrical power for whatever reason. In pneumatically controlled systems, a spring is inherent and simple, but in electronic actuators with a spring, extra power is required both to do the work and to spring the gear motor through its gear train (see e.g. Canadian Patent No. 686,557 of Enghold, issued May 12, 1964), or use a clutch (see e.g. laid-open Canadian Patent Application No. 2,155,466 of Birchmeier) or time delays result while a capacitor or battery recharges. In general such systems create additional complexity and extra costs. In smaller actuators, free running hysterysis type motors with gear trains are able to be sprung back through their travel and gearing to spring shut by a carefully sized and selected spring. But in larger actuators, more powerful motors and specifically DC motors, synchronous motors, or motors which have inherent friction, magnetic "locking" and/or resistance and friction of brushes or commutators, etc., all add up as resistance to springing backwards to the safe position. The gearing and motor friction is such that the spring cannot return these actuators and/or alternatively they slam shut against the end stop, thus breaking the gearing or linkage mechanism. In other variations, clutches have been incorporated, but the force of the return spring can be so great as to constitute a danger, or to cause water hammer in valved applications. To solve this problem, miniature hydraulic pistons, weighted speed governors, brakes, or other speed controllers have been added at further increased complexity and cost just to control slamming or excessive speed.
Canadian Patent No. 686,557 of Engholdt issued May 12, 1964 teaches a valve system in which the valve is kept open by an electrically operated motor during normal power conditions, but a spring closes the valve when power to the motor is interrupted. Reduction gearing is provided between the motor and actuating mechanism for the valve to enable a motor of relatively small size to be utilized to actuate the valve. The motor, of free-wheeling type, is forced backwards by the spring as it closes the valve.
Baumann U.S. Pat. Nos. 4,613,798 issued Sep. 23, 1986 and 4,677,355 issued Jun. 30, 1987, laid-open Canadian application Serial No. 2,155,466 of Birchmeier published Feb. 18, 1996 and Australian Patent No. 467,591 of Carroll as well as Canadian Patent No. 1,087,680 of Waltham issued Oct. 14, 1980 teach electric motor controlled positioning devices, the positioning devices being returned to safety position under urging of a spring if there is a power failure whereupon the motor free-wheels back through its gearing.
Teaching capacitive power backup to drive an actuator motor to a fail-safe location of a positioning device are U.S. Pat. Nos. 5,744,876 of Fangio issued Apr. 28, 1998, 5,744,923 of Strauss et al issued Apr. 28, 1988 and 5,278,454 of Strauss et al issued May 23, 1995 (upon re-examination), as well as Canadian applications Serial Nos. 2,146,413 of Jatnieks, published Oct. 7, 1995 and 2,138,655 of Strauss et al published Jan. 6, 1994. Laid-open Canadian applications Nos. 2,007,427 of Brown et al published Jul. 23, 1990 and 2,039,884 of Shah published Oct. 6, 1992 teach the use of capacitive power to change the direction of a motor.
Of general background interest teaching general types of fail-safe devices for positioning components are U.S. Pat. Nos. 4,129,811 of Pearson issued Dec. 12, 1998 (emergency door opening device), and 4,637,296 of Hirosaki et al issued Jan. 20, 1987, and 5,422,808 of Cantanese, Jr. et al issued Jun. 6, 1995, and laid-open Canadian patent application Serial No. 2,136,346 of Hyppio et al published Dec. 9, 1993, 5,144,153 of Scheppmann issued Sep. 1, 1992 (motorized gate control upon power failure) and 5,576,581 of Iannuzzi et al issued Nov. 19, 1996 (door control system).
These references teach relatively complicated mechanical and electro-mechanical solutions for positioning dampers, valves and the like during power interruptions. It is an object of the present invention to provide a relatively simple, economical and effective spring-return type of fail-safe electrically powered actuator for a positioning device.